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Researchers from KCL visited UdG between the 17th and 24th of January, successfully completing work on integrating the controllers of the valve turning scenario into the planning architecture. This involved running the scenario many times during the week, with the Girona 500 AUV.

The scenario begins with a panel, hidden somewhere in the sparsely decorated pool. The AUV is given a set of coordinates at which the panel might be. The planner directs the AUV to search for the panel, move close to inspect the valves, detect their orientation, and finally to turn the valves to the correct configuration.

The architecture was modeled to be robust — replanning when new information is discovered, or the environment does not meet expectations. This means that when the valves do not turn as expected, the Girona 500 AUV would try again and again, grasping persistently with its end effector.

During the week, the two teams met to decide how their collaboration should continue. The next steps will integrate planning with the chain cleaning scenario; further improve the valve turning scenario; and combine both to form a longer, more elaborate mission.

During the last week of November NTUA and UdG members put their efforts together to push forward the autonomous chain cleaning task of the PANDORA Project. To this end it is required to detect the chain links and follow them accurately.

NTUA and UdG teams working at CIRS for the chain following task

UdG team provided a module that performs detections of chain links on the sonar imagery. The chain link detector has been designed to overcome the difficulties of performing object recognition on sonar data (such as the presence of noise, moving shadows or intensity alterations due to viewpoint changes). Taking as input the link detections, NTUA team developed a module that fits a curve through the multiple detections and groups them to obtain a waypoint at the center of each link. The last step that must be performed consists in concurrently follow the identified waypoints while performing new detections. Here, two problems were identified. First, the insonification area of the forward-looking sonar lies always several meters ahead of the vehicle, so the AUV must point on the direction of the last link while keeping its position over the current one. Second, if this two movements are not well coordinated the chain can easily drop off the sonar’s field of view since it is very narrow (30º).

ROS visualization while performing chain following

These algorithms were tested in the UdG water tank using Girona 500 AUV equipped with the ARIS3000 sonar, over a mock up of a chain of 7 meters. Successful results were obtained in the link detection and path generation stages. For the following algorithm new strategies are under development.

One of the demonstrations shown during the first year review was a visual servo control performed by Girona 500 AUV in front of a valve panel. This work has been carried out by the NTUA CSL group together with UdG. Three main algorithms work together to achieve this task: A visual detector identifies the valve panel and computes relative positions to it; an EKF-SLAM algorithm combines these updates with navigation sensor measurements to localize the vehicle while mapping the panel in the world. Finally, a control scheme navigates and stabilizes the vehicle in front of the detected target. The control scheme algorithm has been reported in a paper submitted at IROS 2013.